JP2010540399A - Annealing diamond at low pressure - Google Patents

Abstract

  The present invention relates to a method for improving the optical properties of diamond at low pressure, and more particularly to growing CVD diamond and from about 5 seconds to about 3 in a reducing atmosphere at a pressure of about 1 to about 760 torr outside the diamond stable region. Increasing the temperature of the CVD diamond to about 1400 ° C. to about 2200 ° C. for a time period of time.

Description

Reference to Government Involvement This invention was made with US government support under grant number NSF EAR-0550040 from the National Science Foundation. The US government has certain rights in this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to annealing diamond, and in particular, the low pressure of single crystal CVD diamond, ie, much lower pressure than previously used for annealing single crystal CVD diamond, for example, about 1 atmosphere or less. Relates to annealing at different pressures. The present invention is useful for improving the optical properties of diamond and is particularly useful for the production of high optical quality single crystal CVD diamond at high growth rates.

2. Description of Related Art Chemical vapor deposition of diamond is achieved by applying energy to a gas-phase carbon-containing precursor molecule. For example, microwave energy can be used to generate a plasma, thereby depositing carbon on the seed diamond to form diamond. Until recently, all CVD techniques for growing diamond yielded polycrystalline diamond or multiple very thin layers of single crystal diamond. The three inventors of this application (i.e., Dr. Hemley, Dr. Mao, and Dr. Yan) have developed microwave plasma CVD techniques for growing large single crystal CVD, and these techniques have been developed in 2002. US patent application Ser. No. 10 / 288,499, filed Nov. 6, 2011, current US Pat. No. 6,858,078, US patent application Ser. No. 11/438, filed May 23, 2006. 260, U.S. patent application Ser. No. 11 / 599,361, filed Nov. 15, 2006, all of which are incorporated herein by reference.

  In our microwave plasma CVD technique, single crystal diamond can be grown on seed diamond, eg, yellow type Ib HPHT synthetic diamond, at a rate of 150 μm or more per hour. The color of diamond produced by our microwave plasma CVD technique depends on the temperature at which the diamond grows. In particular, when diamond grows within a specific temperature range, this depends on the gas mixture in the plasma, but colorless diamond can be produced. However, diamonds produced at temperatures outside this specific range can be yellow or brown.

  Browning lightening of brown natural diamond by high temperature and high pressure annealing and reduction of impurities have been reported in I. M. Reinitz et al., Gems & Gemology 36, 128-137 (2000).

  Most natural diamonds are brown, which reduces their attractiveness as gems (eg, Fritsch E., GE Harlow (edited) (1998), “The Nature of Diamonds”, Cambridge University Press, UK , 23-47 HPHT annealing is the current commercial method for improving the color of natural brown diamonds since 1999, which range from 1800-2500 ° C. to prevent diamond graphitization. Temperature and high pressure within the range of 5 GPA, eg AT Collins, H. Kanda, and H. Kitawaki, “Color change produced in natural brown diamonds by high-pressure, high-temperature treatment”, Diamond Relat Mater. 9, 113-122 (2000); Alan T. Collins, Alex Connor, Cheng-Han Ly, Abdulla Shareef, Paul M. Spear, "High-temperature annealing of optical centers in type-1 diamond", J. Appl. Phys. 97, 083517 (2005); D. Fisher and And R. A. Spits, Gems. Gemol. 36, 42 (2000)). The brown reduction seen in low nitrogen natural diamonds is due to annealing of plastic deformation (see, eg, LS Hounsome et al., “Origin of brown coloration in diamond”, Physical Review B 73, 125203 (2006)). ). In the nitrogen-containing diamond, vacancies generated by the dislocation during the annealing are trapped to form an NVN center, and the neutrally charged H3 band makes the diamond a yellow-green color.

  A few natural brown diamonds have been made colorless or nearly colorless by high temperature treatment (> 700 ° C.) (eg Ming-sheng Peng et al. “Studies on color enhancement of diamond”, Hunan Geology Supp, 17-21 (1992 )).

The following defects are observed in nitrogen-doped SC-CVD diamond. Substituted nitrogen (Ns ⁰ and Ns ⁺ ), nitrogen-vacancy complex (NV ⁻ and NV ⁰ ), nitrogen-vacancy-hydrogen (NVH ⁻ ), vacancy-hydrogen complex, silicon-vacancy complex, and Non-diamond carbon.

  U.S. Pat. No. 7,172,655 relates to a method for producing single crystal CVD diamond of a desired color, for example in the range of pink to green.

Three of the present inventors used a reaction vessel in a conventional high-temperature and high-pressure apparatus to convert a single crystal brown CVD diamond into a colorless transparent single crystal diamond, a temperature of 1800-2900 ° C. and 5-7 GPa. Discloses HPHT annealing of single crystal yellow or brown CVD diamond for about 1-60 minutes at pressure (see US patent application Ser. No. 10 / 889,171 filed Jul. 13, 2004). . More specifically, Drs. Hemley, Dr. Mao, and Dr. Yan at least 4.0 GPa outside the diamond stable region in an atmosphere having a N ₂ / CH ₄ ratio of 4-5% at a temperature of about 1400-1460 ° C. It has been discovered that at pressure, single crystal yellow or light brown CVD diamond grown at a high growth rate can be annealed into colorless single crystal diamond. The Raman and PL spectra of CVD diamond thus annealed reveal the disappearance of hydrogenated amorphous carbon in such colorless single crystal diamond and the significant NV impurities in such colorless single crystal diamond. A decrease was shown. These changes appear to be similar to the improved transparency obtained by HPHT annealing of brown natural diamond reported by IM Reinitz et al.

  The high pressure associated with the results of the above method can be expensive. Accordingly, it is desirable to develop a low pressure annealing method for diamond to improve certain characteristics of diamond, such as optical properties. It would also be desirable to develop low temperature annealing methods that can be used for various types of diamond, such as, but not limited to, CVD diamond (single crystal and polycrystalline diamond), HPHT diamond, and natural diamond.

  The object of the present invention is to improve the optical properties of diamond. Another object of the present invention is to lighten or eliminate the color of the diamond. Yet another object of the present invention is to improve the quality of all kinds of diamonds, including but not limited to single and polycrystalline CVD diamond, HPHT diamond, and natural diamond. A further object of the present invention is to achieve these objects by a method operated at low pressure. Other objects will become apparent from the following description of the invention.

SUMMARY OF THE INVENTION Broadly speaking, the present invention relates to a method for annealing diamond or a method for improving the optical properties of diamond to substantially eliminate one or more problems due to limitations and disadvantages of the related art. .

  Additional features and advantages of the invention will be set forth in the description which follows, and will be apparent from the description, or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof.

  In order to achieve these and other advantages, according to the object of the invention, which is embodied and outlined, a method for improving the optical quality of diamond raises the temperature of the diamond from about 1000 ° C. to about 2200 ° C. And controlling the pressure of the diamond to about 5 atmospheres or less outside the diamond stability region. The above conditions are controlled under a reducing atmosphere, and the diamond is held in a heat sinking holder that forms thermal contact with the side of the diamond adjacent to the edge of the diamond.

A method for producing CVD diamond, wherein the temperature of the growing diamond crystal is in the range of 900-1400 ° C., and has a high melting point and high thermal conductivity in order to minimize the temperature gradient across the diamond growth surface. By mounting the diamond in a heat sink holder made of material, the step of controlling the temperature of the growth surface of the diamond and in the deposition chamber having an atmosphere exceeding 150 torr by microwave plasma chemical vapor deposition on the growth surface of the diamond And growing the single crystal diamond in a heat sink holder, wherein the atmosphere comprises CH ₄ from about 8% to more than about 30% per unit of H _2; Step out of the chamber and diamond And increasing the temperature of the CVD diamond from about 1400 ° C. to about 2200 ° C. for a time of about 5 seconds to 3 hours in a reducing atmosphere at a pressure of about 1 to about 760 torr outside the constant region. Disclose. The CVD diamond produced by the above method may be a single crystal CVD diamond.

  It is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed invention.

FIG. 5 is a graph of growth rate versus single crystal CVD diamond color, with some diamonds annealed by the low pressure high temperature method of the present disclosure to improve optical quality. It is a photograph of CVD diamond before and after low-pressure annealing treatment. 2 shows UV-VIS absorption spectra of diamond before and after annealing. 2 shows photoluminescence spectra of brown diamond before and after annealing. 5a and 5b show the infrared absorption spectra of diamond before and after annealing.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the preferred embodiments of the invention.
The method of the present invention has substantially two parts. The first is a low pressure method that anneals diamond or improves its optical properties, and the second is a) growing single crystal diamond, preferably single crystal diamond, preferably by microwave plasma chemical vapor deposition. A two-stage process for rapidly producing high optical quality diamonds by steps and then b) performing annealed diamond or performing a low pressure process to improve chemistry. The latter method is particularly useful as long as the production of poorly colored diamonds (eg brown diamonds) is a means of improving the quality of CVD diamond grown rapidly at a common rate.

  The term “anneal” as used when referring to the method of the present application is intended to improve certain properties of diamond, such as, but not limited to, reducing residual stress, removing defects, and It should be understood as performing removal. For example, annealing should be understood to improve the optical quality of diamond.

  Diamond high temperature low pressure annealing methods (hereinafter also referred to as “HT” annealing or “HT” methods) can be any type of diamond, including, but not limited to, single crystal CVD diamond, polycrystalline CVD diamond, HPHT diamond, and This can be done for natural diamonds. In a preferred embodiment, the method of annealing the diamond or improving the optical properties of the diamond is performed using CVD diamond. In a more preferred embodiment, the method is performed using single crystal CVD diamond.

  The heating source used to raise the diamond temperature in the low pressure high temperature annealing method includes, but is not limited to, a microwave, hot filament, heating furnace, or oven heating source.

  Low pressure high temperature annealing can improve the color of the diamond by at least three grades. For example, when the brown K grade color is annealed, it can be improved to the G grade. The brown G grade color can be improved to the E to F grade having a pink color with a transmittance of about 550 nm by the annealing treatment. Such color enhancement results in comparable results to those achieved by the high temperature and low pressure method of the present invention using, for example, the high temperature and high pressure annealing method disclosed in US patent application Ser. No. 10 / 889,171. It is shown that.

  The color is evaluated by 100% normalized transmission at 800 nm and according to the transmission of 80, 70, 60, 50, 40, 30, 20, 10, 0% respectively at 400 nm, E, F, G, H, Values of I, J, K, L, and M are assigned. As described above, the color is improved by three grades by the low pressure and high temperature annealing treatment.

  Referring more specifically to the drawing, FIG. 1 shows a growth rate versus color graph of single crystal CVD diamond, with some diamonds annealed by the low pressure high temperature method of the present disclosure to improve optical quality. I let you. The diamond shown in the graph is a high quality single crystal CVD diamond as a Type I or Type II diamond with nitrogen impurities from less than 10 ppb to more than 400 ppm. These diamonds are over 18 mm (15 carats) thick and can be made using the very fast growth rate methods disclosed, for example, in US patent application Ser. Nos. 11 / 438,260 and 11 / 599,361. Manufactured by the inventors. These diamonds were annealed at a temperature of about 1400 ° C. to about 2200 ° C. for about 5 seconds to about 3 hours. It is understood that the diamond is maintained in a reducing atmosphere of about 1 torr to about 5 atmospheres, thereby preventing significant graphitization of the diamond. In most tests, hydrogen was used to maintain a reducing atmosphere. Diamond heated by microwave plasma CVD is mounted inside a molybdenum holder, an example of which is disclosed, for example, in US Pat. No. 6,858,078. Next, the diamond in the holder is surrounded with graphite powder in order to make the temperature distribution uniform and to prevent etching by microwave plasma and diamond heating to such an extent that cracks occur.

The single crystal CVD diamond treated by the above-described low-pressure high-temperature annealing method has at least one of the following characteristics.
1. Dark diamonds turn colorless or fancy colors, e.g. light pink, red, or purple, almost colorless.
2. The H3 center at 503 nm (nitrogen-vacancy complex), where the PL intensity of the NV center of the original nitrogen-vacancy impurity at 575 nm and 637 nm excited by the laser increased or decreased and did not exist until the annealing step Occurs.
When the aC: H infrared absorption broad band at 3.2930 cm ⁻¹ is annealed, it is well separated, mainly {111} and {100} C— at 2810 cm ⁻¹ , 2870 cm ⁻¹ , and 2900 cm ⁻¹ . H stretching vibration peak. The electronic transition absorption induced by hydrogen at about 7357 cm ⁻¹ , 6856 cm ⁻¹ , and 6429 cm ⁻¹ is greatly reduced.
4). Under a polarizing microscope, less optical birefringence indicates less distortion than the original diamond.
5). The Vickers hardness test shows a reduction in fracture line, indicating higher toughness.

  Diamonds having low and high nitrogen impurities annealed by the aforementioned high temperature low pressure annealing method include, but are not limited to, optical, mechanical and electronic applications, jewelry, laser windows and gain media, heat sinks, quantum calculations, Suitable for use in semiconductors and wear resistant applications.

As seen in Figure 1, the microwave plasma using 50 sccm CH ₄ in brown diamonds grown by microwave plasma CVD using 0.2 sccm N _2, and 0.1 sccm N ₂ in 50 sccm CH ₄ Light brown diamonds grown by CVD (MPCVD) had colors ranging from KM and HK, respectively. After the low pressure and high temperature treatment, the diamond color was in the following range. Brown diamond (G to J) and light brown diamond (EG). This shows that the color enhancement of about three color grades can be realized by performing the low pressure high temperature annealing method of the present invention.

  FIG. 2 shows photographs of MPCVD diamond before and after low pressure high temperature annealing. In three separate photos, the diamond on the left has not been treated with a low pressure, high temperature annealing method. The diamond on the right side is processed by a low pressure high temperature annealing method. The difference in the transparency of the diamond before and after processing is readily apparent from the photographs.

EXAMPLES Various SC-CVD diamonds produced by Carnegie Institution in a very fast growth rate method have the following properties. (1) Nitrogen impurities from less than 10 ppb to more than 400 ppm as measured by secondary ion mass spectrometer (SIMS) measurement, (2) colorless to almost colorless to brown color as type I and type II diamonds, (3 ) Sizes up to more than 18 mm (or 15 carats) thick. These diamonds produced by intentionally adding nitrogen at a temperature of 600-1400 ° C. increase the growth rate, promote {100} facet growth and prevent the formation of twin and polycrystalline diamonds. It has been shown. The intensity of brown is largely dependent on temperature and nitrogen concentration in the gas. Nearly colorless to brown SC-CVD diamond can be produced with a nitrogen concentration of less than 2% N ₂ / CH _{4 and} has a clear non-diamond carbon band around 1500 cm ^{−1 in} Raman excited by the 514 nm laser spectrum. dark brown diamonds brown with can be prepared in _{20% ~1000% N 2 / CH} 4.

  The brown diamond was annealed in a microwave plasma CVD chamber at a high temperature from 1400 to over 2200 ° C. for a time from 2 hours to less than 1 minute at a hydrogen gas pressure of 200 torr. These diamonds are heated by the microwave plasma CVD method to prevent uniform heating and to prevent diamond heating that can cause local etching by microwaves and plasma and thermal cracking. Placed inside a molybdenum holder surrounded by graphite powder.

  Brown and tough SC-CVD diamonds prevent significant graphitization and cracking that occur at high temperatures (eg, above 1600 ° C.), low pressures outside the diamond stability pressure, and high energy hydrogen plasma etching conditions. It should be noted that it should be a high quality single crystal diamond. Single crystal CVD diamond after high temperature treatment at 1400-2200 ° C. shows a marked improvement in optical, electronic and mechanical properties.

  Forty or more Type II SC-CVD diamond plates produced by HT annealing with a nitrogen impurity content of less than 10 ppm and a thickness of 0.2-3 mm were characterized as follows.

  I. UV-VIS absorption: After HT treatment, the brown diamond turned colorless or nearly colorless with a fancy color, such as light pink, red, purple, or orange-pink. As seen in the UV-VIS absorption spectrum in FIG. 3, dark diamonds typically have three broad absorption bands in the visible region: 270 nm substitutional nitrogen absorption, 370 and 550 nm, but a wide band after HT annealing. Decrease. Similar color enhancements have been reported in HPHT annealing. The color grade improves on average from 3 grades, for example from J color to G color, and these grades are evaluated from the absorption spectrum. No significant color improvement of CVD diamond was observed for diamond annealed at atmospheric pressure below 1500 ° C.

II. Photoluminescence: The brown CVD diamond photoluminescence (PL) spectrum seen in FIG. 4 shows the original nitrogen-vacancy impurities [N−V] ⁰ and [N−V] ⁻ at 575 nm and 637 nm excited by the laser. It is shown that the H3 center (nitrogen-vacancy complex) at 503 nm, which did not exist before HT annealing, has begun to appear. There are two stages at the NV center when performing HT annealing. After annealing at a lower temperature or for a shorter time, the PL intensity of the [N-V] ⁰ (575 nm) and [N-V] ⁻ (637 nm) centers increased 1 to 5 times, and due to excitation at 488 nm Strong orange fluorescence is obtained. Before annealing, the as-grown brown diamond shows dark red fluorescence. It is thought that the hue of orene in HT annealed CVD diamond is derived from this orange fluorescence. At higher temperatures or longer annealing times, the PL strength of [N−V] ⁰ and [N−V] ⁻ centers is reduced. Unlike HPHT processing, NV centers associated with quantum computer applications are clearly diminished or disappeared and are dominated by strong H3 centers in the PL spectrum. [N-V] ^- it is part of the center (637 nm) tends to decrease. This is primarily [N-V] ^- By unbonded electrons from the center to form a 575 and H3 centers begin to bond, the content of the electronic center is reduced, that is associated with improvement in their order color May mean.

III. Infrared absorption: The infrared absorption spectrum reveals vibrations associated with hydrogen and changes in the electronic structure after HT annealing. FIG. 5 shows a C—H stretching vibration band in the range of 2800 to 3200 cm ⁻¹ . A broad band at 2930 cm ⁻¹ attributed to hydrogenated amorphous carbon (aC: H) is observed in brown CVD diamond. This strength correlates with the brown color of diamond and its high toughness. a-C: H peak by HT annealing, (sp ³ hybridized bonds on ^{{111}) 2810cm -1, 2870} (sp 3 -CH 3), and sp ³ hybrid bonds on ^2900cm -1 ({100} ), 2925 (sp ³ —CH ₂ —), 2937 and 2948 cm ⁻¹ , 3032 and 3053 cm ⁻¹ (sp ² hybrid bonds), the C—H stretch bands were sufficiently separated. The {111} face during CVD is a locally denser structure with a relatively open aC: H structure with dangling bonds in as-grown brown {100} CVD diamond but with enhanced color upon annealing. (2) shows the change. A possible mechanism for color enhancement has been described based on the observation of C—H stretching of CVD diamond that is HPHT annealed. In electronic transitions within region (Fig. ^{5b), 7357cm} -1 ^(0.913eV, hydrogen induced electronic ^{transitions),} 7220cm -1, large absorption, and a small absorption greatly reduced in 8761 and 5567cm ^-1 in 6856 and 6429cm ^-1 Or disappear. Furthermore, the continuously increasing absorption of 5000 to 10000 cm ^{−1 in} the near infrared region decreases. The effect of the above HT annealing is similar to the effect of HPHT annealing. One exception is that HT diamond and raw material CVD diamond have 3124 cm ⁻¹ peaks (H containing 1 C) and 7357 cm ⁻¹ , 7220 cm ⁻¹ , 6856 and 6429 cm ⁻¹ , but HPHT diamonds It is not having. Furthermore, HT diamond does not have 3107 cm ⁻¹ (sp ² —CH═CH—) associated with gray and is present in HPHT annealed samples, 2972 (sp ² —CH ₂ — (28)) and 2991 cm ^{−. 1} is the same. Another difference that can occur is that the sp ³ C—H bond shift induced by high pressure is 3-15 cm ⁻¹ higher in wavenumber, with HPHT anneal samples 2820 cm ⁻¹ , 2873 cm ⁻¹ , and 2905 cm ^−1. It becomes.

  IV. Birefringence: Under the microscope using crossed polarizers, HT annealed diamonds show lower optical birefringence, indicating less distortion than the original unannealed diamond, which The fact that the vote turns from yellow to gray and the two cross-direction strains become one direction further illustrates the reduction in stress.

Comparing the CVD diamond characterization before and after HT annealing with HPHT annealing reveals the annealing mechanism and the cause of brown and pink colors. Based on the UV-VIS, PL, and SR-FTIR spectra, the mechanism underlying the high temperature annealing of CVD brown diamond can be deduced. As the annealing temperature is increased, the PL and SR-FTIR spectra show that there are three important steps in the color change. In the first stage, when the temperature reaches 700 ° C., the vacancies can move, and the vacancies are captured at the Ns center, so that more NV centers are formed. Presumably, this is believed to be the reason why the NV ⁰ and NV ^- center PL intensities increase after lower temperature or shorter time annealing. Until 1400, the brown color still does not decrease. Second, when heated to 1400 ° C, the color change begins. It is speculated that this is because hydrogen can move at this temperature. It has been found that when polycrystalline CVD diamond is annealed at 1700 K (1400 ° C.), some of the hydrogen on the internal grain boundaries or in the intergranular material can move. See DF Talbot-Ponsonby, ME Newton, JM Baker, GA Scarsbrook, RS Sussmann, and AJ Whitehead. Phys. Rev. B 57, 2302-2309 (1998). Thus, in the FTIR spectrum, aC: H decreases and hydrogen forms C—H bonds on {100} and {111}. First-principles modeling studies show that hydrogen can inactivate the optical activity of {111} -hole disks. See LS Hounsome et al., “Origin of brown coloration in diamond”, Physical Review B 73, 125203 (2006). If the absorption at 550 nm increases or remains unchanged while the absorption at 270 and 370 nm decreases, the result is a pinkish brown, orange brown or purple color. A mirror symmetry relationship can be seen between the absorption band at 550 nm and the NV center emission bands at 575 and 637 nm. This appears to indicate that the absorption at 550 nm is caused by the NV center. Thus, the pink hue of CVD diamond is caused by a stable NV center.

  The best color enhancement is observed at temperatures above 1700 ° C., which makes the brown color pink, colorless, or nearly colorless, or light pink / green. One possible reason is that vacancies are more easily trapped by hydrogen than nitrogen at the temperature at which more hydrogen atoms move, and at the same time Ns also moves at this temperature to form agglomerated H3. This is because the stable NV center anneals. Another possible change is a decrease in hydrogen. Even after higher temperature annealing (1800-2200 ° C.), a lower intensity of C—H stretching vibration absorption can be observed. This probably indicates the breaking of the CH bond.

There are three factors associated with the brown color of CVD diamond: nitrogen, vacancies, and hydrogen. The brown intensity of as-grown CVD diamond depends on the nitrogen concentration in the gas. [NV] ⁰ (575 nm) and [NV] ⁻ (637 nm) The brown color also becomes darker when the original PL intensity of the center is increased with as-grown CVD diamond. When the diamond becomes nearly colorless or colorless upon annealing, the NV center decreases or disappears. When the aC: H peak in brown CVD diamond is annealed at high temperature and pressure, the absorption of various well-separated C-H stretching bands and hydrogen-induced electronic transitions is reduced. The electronic transition absorption induced by aC: H peaks and hydrogen is very little or absent in colorless as-grown CVD diamond.

Compared to CVD diamond HPHT annealing, the high temperature low pressure method is much less expensive. There is also a high degree of freedom with respect to sample size, because during HPHT processing, thin plates crack and large samples over 10 cm cubic cannot be installed in the HPHT press. In addition to color enhancement, the high temperature low pressure annealing method can produce diamond with low and high nitrogen impurities. One potential use for such diamonds is in quantum computers. Pink diamond is considered promising as a host for quantum computers. NV ^- spin has obtained most of what is required for practical qubits and has been extensively studied in connection with quantum computing. Based on absorption and emission, it can be concluded that the pink color of CVD diamond originates from the NV center. Pink CVD diamond produced by high-temperature and low-pressure annealing has increased NV center strength as compared to as-grown CVD diamond, whereas such an HPCH method disappears due to annealing. Therefore, the strength of the NV center can be controlled by the high temperature low pressure annealing method. Therefore, high temperature low pressure annealed pink CVD diamond should become a promising material for quantum computers in the future.

  The present invention may be embodied in a number of forms without departing from the spirit and substantial characteristics of the invention, but unless otherwise specified, the above embodiments are in any of the details of the above description. It is not intended to be limiting, but should be construed broadly within the spirit and scope of the invention as defined in the appended claims, and thus the boundaries and limitations of the claims, or such boundaries and limitations. It should also be understood that any changes and modifications that fall within the scope of the equivalents are therefore intended to be embraced by the appended claims.

Claims (23)

A method for improving the optical properties of diamond, comprising:
(I) raising the temperature of the diamond to about 1000 ° C. to about 2200 ° C .;
(Ii) controlling the diamond pressure to about 5 atmospheres or less outside the diamond stability region;
The pressure is controlled in a reducing atmosphere;
The method wherein the diamond is held in a heat sinking holder that forms thermal contact with a side of the diamond adjacent to an end of the diamond.   The method of claim 1, further comprising surrounding the diamond in the heat sinking holder with a powder having a melting point greater than 2500 degrees Celsius.   The method of claim 2, wherein the powder comprises graphite.   The method of claim 1, wherein the diamond is CVD diamond.   The method of claim 4, wherein the CVD diamond is single crystal CVD diamond.   The method of claim 1, wherein the temperature of the diamond is raised to about 1400C to about 2200C.   The method of claim 1, wherein the pressure is maintained between about 1 torr and about 760 torr.   The method of claim 1, wherein the diamond temperature is increased using a group of heat sources consisting of microwave, hot filament, furnace, torch, and oven heat sources.   The method of claim 8, wherein the temperature of the diamond is increased using a microwave source.   The method of claim 5, wherein the CVD diamond is a single crystal coating on another material.   The method of claim 5, wherein the single crystal CVD diamond is initially brown and colorless.   The method of claim 2, wherein the heat sinking holder is composed of molybdenum. A method for producing CVD diamond of desired optical quality comprising:
i) in a heat sink holder made of a material having a high melting point and high thermal conductivity, so that the temperature of the growing diamond crystal is in the range of 900-1400 ° C. and minimizes the temperature gradient across the growth surface of the diamond. Controlling the temperature of the growth surface of the diamond by mounting the diamond on the surface;
ii) growing diamond on the growth surface of diamond by microwave plasma chemical vapor deposition in a deposition chamber having an atmosphere greater than 150 torr, wherein the atmosphere is from about 8% per unit H ₂ Including up to more than about 30% CH ₄ and less than about 2% to more than about 1000% N ₂ per unit of CH ₄ ;
iii) removing the grown CVD diamond from the chamber while maintaining it in the heat sink holder;
iv) increasing the temperature of the CVD diamond from about 1400 ° C. to about 2200 ° C. for a period of about 5 seconds to 3 hours in a reducing atmosphere at a pressure of about 1 to about 760 torr outside the diamond stable region; Including.   In step iv), the method further comprises surrounding the diamond in the heat sinking holder with a powder having a melting point greater than 2500 ° C before raising the temperature of the CVD diamond from about 1400 ° C to about 2200 ° C. Item 14. The method according to Item 13. A method for producing single crystal CVD diamond of desired optical quality, comprising:
i) in a heat sink holder made of a material having a high melting point and high thermal conductivity, so that the temperature of the growing diamond crystal is in the range of 900-1400 ° C. and minimizes the temperature gradient across the growth surface of the diamond. Controlling the temperature of the growth surface of the diamond by mounting the diamond on the surface;
ii) growing single crystal diamond on said growth surface of diamond by microwave plasma chemical vapor deposition in a deposition chamber having an atmosphere greater than 150 torr, said atmosphere being about 8 per unit H ₂ From about 2% to more than about 30% CH _4, comprising less than about 2% to more than about 1000% N ₂ per unit of CH ₄ ;
iii) removing the grown single crystal diamond from the chamber;
and iv) improving the optical quality of the diamond by the method of claim 6. A method for producing CVD diamond, comprising:
i) growing CVD diamond;
ii) increasing the temperature of the CVD diamond to about 1400 ° C. to about 2200 ° C. at a pressure of about 1 to about 760 torr outside the diamond stable region, for a time between about 5 seconds and about 3 hours in a reducing atmosphere. Including.   A single crystal CVD diamond produced by the method of claim 15.   A CVD diamond produced by the method of claim 16.   16. Single crystal CVD diamond produced by the method of claim 15 having a color of F or less.   The single crystal diamond produced by the method of claim 15, wherein as a result of step iv), N-V centers increase or decrease or disappear, or H3 centers with strong photoluminescence spectrum predominate. .   The single crystal produced by the method according to claim 16, wherein, as a result of step ii), the N-V center increases or decreases or disappears, or a strong H3 center predominates in the photoluminescence spectrum. diamond. The single crystal diamond produced by the method of claim 15 having infrared absorption peaks at about 3124, 7357, 7220, 6856, and 6429 cm ⁻¹ . The single crystal diamond produced by the method of claim 16 having infrared absorption peaks at about 3124, 7357, 7220, 6856, and 6429 cm ⁻¹ .